I equate ball pocketing and dwell time in a string/frame combination and consider it a good thing. As in like what gut does.

The question is: Does increased ball pocketing and thus dwell time equal more spin potential?

Reading the threads on rackets that provide more spin potential, fewer strings are usually, but not always, cited as providing more spin potential. Is this perhaps because the ball penetrates farther into the stringbed and has more string in contact around it to impart spin?

However when I read threads on Polys, which would have the least ball pocketing and dwell time, most of them claim to produce more spin than other kinds of strings. True? Not true?

Dwell time is a subjective sensation and nothing more. The ball is on the stringbed for such a short period of time that your brain literally does not even get the information that there was a ball on the strings until after you've hit it.

It's largely irrelevant whether the human brain can sense ball impact as it's occuring. It's not like you're gonna change your swing during the split second of impact. (Except for touch volleys.)

In fact, your nervous system is fast enough to detect the split second the ball hits the racket. The nervous system is ridiculously fast. The basis for touch/drop volleys is softening up on the grip during impact, so the ball dies.

OK. Maybe my brain is not fast enough to recognize dwell time, but it is a major parameter for TW string data, so it must be indicative of something.

The difference between a really tight poly bed and user friendly gut is very noticable and would seem to imply longer contact times with a more resilient string. Correct?

My understanding of spin is that it is produced by the movement of the racquet while the ball is in contact with the stringbed in such a way that imparts rotation. The longer the contact, the more rotation should be imparted?

OK. Maybe my brain is not fast enough to recognize dwell time, but it is a major parameter for TW string data, so it must be indicative of something.

The difference between a really tight poly bed and user friendly gut is very noticable and would seem to imply longer contact times with a more resilient string. Correct?

My understanding of spin is that it is produced by the movement of the racquet while the ball is in contact with the stringbed in such a way that imparts rotation. The longer the contact, the more rotation should be imparted?

Thanks,

Harry

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On a high speed camera you can see how mains are sliding on impact if you hit a top spin shot. That means, the ball slides first and then displaces the mains. When mains snap back, they launch the ball back at certain angle. All of this takes time, dwell time. And of course the frame itself is deformed under pressure, and stringbed too, while ball is sliding on the string surface.
The sharper the poly, the longer it can be pushed by the ball if the cross string is sleek enough. It takes less effort to displace natural gut due to high elasticity, especially on a sleek cross string, hence you can get quite a spin from the smooth natural gut string, but not from the smooth multi (not enough elasticity to easily slide back and forth).

On a high speed camera you can see how mains are sliding on impact if you hit a top spin shot. That means, the ball slides first and then displaces the mains. When mains snap back, they launch the ball back at certain angle. All of this takes time, dwell time.
The sharper the poly, the longer it can be pushed by the ball if the cross string is sleek enough. It takes less effort to displace natural gut due to high elasticity, especially on a sleek cross string, hence you can get quite a spin from the smooth natural gut string, but not from the smooth multi (not enough elasticity to easily slide back and forth).

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hope you don´t mind if i join the discussion
if i understand you correctly, your point is that the smoother the strings are, the more topspin they produce? provided they snap back(poly more so, multi less)

It's largely irrelevant whether the human brain can sense ball impact as it's occuring. It's not like you're gonna change your swing during the split second of impact. (Except for touch volleys.)

In fact, your nervous system is fast enough to detect the split second the ball hits the racket. The nervous system is ridiculously fast. The basis for touch/drop volleys is softening up on the grip during impact, so the ball dies.

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Edit: not even worth it.

To the OP: dwell time is not an important TW parameter because there is no way to state it as the measure of anything. The TW spin parameters are stiffness, ball-string friction, string-string friction and perhaps one more. None are quantified as the time the ball spends on the strings.

hope you don´t mind if i join the discussion
if i understand you correctly, your point is that the smoother the strings are, the more topspin they produce? provided they snap back(poly more so, multi less)

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The smoother/sleeker the CROSS strings are and the sharper or more elastic MAINS, the more spin you can get. Or enter super open string patterns to reduce friction with crosses.

thanks, i think i get that.
where does rough poly come in(as in alu power rough or msv hex,...)
in regard of spin? in the mains? is that what you mean by sharper?

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Rough poly is exploiting the ball-string friction parameter. The higher this is, the greater the spin potential. The lower the string-string friction, the greater the spin potential. Interestingly, we have two counter examples to look at then using the same set of data. A stiffer string, according to TWU data, is more likely to be a better spin string. Thereby poly will provide more spin potential than synthetic gut or multifilaments. However, a moreelastic string will also provide more spin potential. These two concepts are not the same. To make it more clear, let me define the two. Stiffness is the ability for a material to not deform or to resist deformation when under stress. Elasticity is the ability for the material to return to its original state after being deformed by stress. So, we're at an impasse: we want a string which does not deform under stress, but one which when it does deform, it returns to its original shape. This is why polyester is so popular for spin. It is very stiff, but yet it has a surprising amount of elasticity.

Once that elasticity is gone from usage, then the string's performance is lessened. If you have a rough string which can hold onto the ball while the string is deforming, you can return more energy to it. BUT! If the sliding friction is too high, or the friction trumps the string's elasticity, then it doesn't matter as much. That's why while natural gut is overall the best for spin next to poly, it still suffers from high string-string friction. Therefore, you want something with elasticity in the mains that bites onto the ball and something smooth in the crosses so that the mains can move more freely. This is the reasoning behind the gut/poly hybrid. If you put a rough poly main with a smooth poly cross, you can theoretically get similar results: you get great stiffness from the mains, and good ball-string friction, and low sliding friction just like with gut/poly.

Dwell time is a subjective sensation and nothing more. The ball is on the stringbed for such a short period of time that your brain literally does not even get the information that there was a ball on the strings until after you've hit it.

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But you remember it for the next time around. That is how it is objective and not subjective.

Rough poly is exploiting the ball-string friction parameter. The higher this is, the greater the spin potential. The lower the string-string friction, the greater the spin potential. Interestingly, we have two counter examples to look at then using the same set of data. A stiffer string, according to TWU data, is more likely to be a better spin string. Thereby poly will provide more spin potential than synthetic gut or multifilaments. However, a moreelastic string will also provide more spin potential. These two concepts are not the same. To make it more clear, let me define the two. Stiffness is the ability for a material to not deform or to resist deformation when under stress. Elasticity is the ability for the material to return to its original state after being deformed by stress. So, we're at an impasse: we want a string which does not deform under stress, but one which when it does deform, it returns to its original shape. This is why polyester is so popular for spin. It is very stiff, but yet it has a surprising amount of elasticity.

Once that elasticity is gone from usage, then the string's performance is lessened. If you have a rough string which can hold onto the ball while the string is deforming, you can return more energy to it. BUT! If the sliding friction is too high, or the friction trumps the string's elasticity, then it doesn't matter as much. That's why while natural gut is overall the best for spin next to poly, it still suffers from high string-string friction. Therefore, you want something with elasticity in the mains that bites onto the ball and something smooth in the crosses so that the mains can move more freely. This is the reasoning behind the gut/poly hybrid. If you put a rough poly main with a smooth poly cross, you can theoretically get similar results: you get great stiffness from the mains, and good ball-string friction, and low sliding friction just like with gut/poly.

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great info, thanks. when i saw your long post, i thought it would go over my head, but you explained it very clearly.
when people say, that a poly is dead, are they then referring to the fact, that it loses the elasticity to snap back?

But you remember it for the next time around. That is how it is objective and not subjective.

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No. Objective is that the stiffness of the string is x. Its dwell time depends on the stroke type, the frame, tension, etc. It's a feeling, and cannot be measured. People on here often say x string has great dwell time, and then others disagree. If it was objective, then there wouldn't be a disagreement. All parameters that we look for in strings are subjective, but most are based on objective things. Comfort, power, spin, control, these are all subjective things. Stiffness, tension stability, durability and cost don't change depending on the player (durability is a bit of a stretch, but a 1.35mm poly is going to last longer for all players than a 18g syn gut). This is why we talk about spin potential, energy return, stringbed stiffness, etc. These things are more or less measurable and give an objective view of what we really feel.

great info, thanks. when i saw your long post, i thought it would go over my head, but you explained it very clearly.
when people say, that a poly is dead, are they then referring to the fact, that it loses the elasticity to snap back?

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No prob! I should state at this point that I DO understand dwell time and that some strings provide more than others. It's just a certain feeling that you get. The reason I'm going on about this is because it's misleading to discuss it as though it changes your amount of control over your shots. Crisp and responsive strings don't exhibit it, but softer strings tend to.

thanks, really appreciate that you took the time to explain that to me.
i got a recommendation to try black widow a while ago. i guess i´ll try that combo with a smooth poly.

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It also works with some sleek synthetic gut cross, such as Gosen OG Sheep Micro or maybe Babolat Nvy. Then you have spin and comfort for at least 3 hitting sessions, until those sharp edges smooth out plus string loses its elasticity.

Dwell time is a subjective sensation and nothing more. The ball is on the stringbed for such a short period of time that your brain literally does not even get the information that there was a ball on the strings until after you've hit it.

No. Objective is that the stiffness of the string is x. Its dwell time depends on the stroke type, the frame, tension, etc. It's a feeling, and cannot be measured. People on here often say x string has great dwell time, and then others disagree. If it was objective, then there wouldn't be a disagreement.

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Most people here are not pros with a highly developed sense of feel.

Dwell time can and has been measured with high-speed photography and is about 4 milliseconds.

It also works with some sleek synthetic gut cross, such as Gosen OG Sheep Micro or maybe Babolat Nvy. Then you have spin and comfort for at least 3 hitting sessions, until those sharp edges smooth out plus string loses its elasticity.

Dwell time can and has been measured with high-speed photography and is about 4 milliseconds.

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Precisely my point. What is being discussed is a sensation: the sensation that the strings are cupping the ball or that the ball is sinking into the strings. The amount of time that the ball is on the stringbed is more or less the same regardless of string type.

Yup, as surehs said, the actual contact time is only a few 1/1000 of a second. The absolute maximum that a nerve impulse can travel is about 120m/s. That's the max velocity of neurons. In actuality, touch neurons travel around 75m/s and pain signals are much much slower. But even using a blazing fast 100m/s impulse that means that, assuming your hand is 1m from your brain, that it still takes 1/100 of a second to get there. That's over twice as long as the ball is on the strings. So literally, the ball is off the strings by the time the signal has reached your shoulder joint, so it is truly gone before you know it. That's not even including the time it takes to process the sensations from the thousands of receptors in your hand. So unfortunately for UCSF, it is impossible for you to change your grip as you're hitting the ball unless you started doing it before the ball was even close to your body.

Precisely my point. What is being discussed is a sensation: the sensation that the strings are cupping the ball or that the ball is sinking into the strings. The amount of time that the ball is on the stringbed is more or less the same regardless of string type.

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Your point is a stupid one. Dwell time is not a sensation. A ball hitting a tennis racket produces a sensation, but that doesn't mean dwell time is a sensation. You may feel a sensation indicative of dwell time, but that's something else.

Dwell time is a property between the strings and the ball. It's irrelevant whether a player can feel it. Even in a person with anesthesia (unable to feel the ball impact) the ball will sit on the strings for a certain amount of time.

"The dwell time of the ball on the strings should increase as the inverse of the square root of the tension; measurements made in the lab bear this out. In addition, the dwell time of the ball on the strings decreases the harder the ball is hit, because the strings become effectively stiffer the more they are forced to deform...
The actual time of contact for a normal shot with normal string tension is about 4 or 5 thousandths of a second. By reducing the string tension and not hitting hard you might be able to increase the dwell time to about 6 or 7 thousandths of a second... These times are so much shorter than your reaction or reflex time that you cannot possibly do anything to change [the way you are hitting] the shot while the ball is on the strings... A longer dwell time also means that the shock of the ball being hit is spread over a longer time; the magnitude of the force at any given time is therefore reduced... If you wish to alleviate arm troubles such as tennis elbow, reducing the tension of your racket strings will not only lessen the initial shock transmitted to your arm but will give you more power from the racket. You will not have to swing so hard, which is kinder to your arm..."

In summary, pvaudio doesn't know jack. And I guess I was wrong about the touch volley exception. Perhaps I was just using a loose grip.

Are you seriously this dense, or do you just enjoy arguing for no reason? Everything you posted, EVERYTHING, supports what I've been saying. Dwell time and ball pocketing as being discussed here are a SENSATION. The fact that Genesis Black Magic and Typhoon produce more dwell time than say Prince Synthetic gut are simply sensational experiences. As your own information posted, the amount of variance in the time the ball spends on the strings is 1-2 milliseconds which you cannot even register. Seriously, I'm doing my best here to not just call you a troll because you do this in every single thread, but it's getting quite annoying. A one millisecond difference in time on the stringbed is measurable ONLY in a controlled situation, and depends on so many factors which vary from player to player, and yet certain strings are said to give more pocketing than others. That is a feeling, and nothing more. Your mind cannot even process a stimulus of 6ms as being longer than one of 4 or 5ms. Nerves simply are not able to respond that quickly. You're arguing as though that increase in contact time is what leads to the sensation of increased ball pocketing. Your nervous system literally is not sensitive enough to register that change. What you're experiencing is a complex series of vibrations and stimuli which give you certain feedback about how you hit the ball. Again, and hopefully for the last time, dwell time, pocketing, whatever you want to call it, is a sensation caused by a complex series of interactions. It is not the fact that the ball is actually sitting on the stringbed significantly longer for certain strings because even using the maximum variance of 3ms as posted in your information would not even register.

OP, let me make this as simple as possible. String up Genesis Typhoon, Dunlop Black Widow or Genesis Black Magic. Go for a hit. You will get that ball pocketing that you're talking about. String up Gosen OGSM. You will not get that same feeling. In both cases, the ball will be on the strings for fractionally longer with the Gosen than with the polys simply because the Gosen is more elastic. This is the point I have been trying to make all along. The sensation of pocketing and dwell is not due to the ball actually being on the strings for a longer period of time, to answer your initial question. It's due to how the strings respond to being hit, and how they send their reaction through the frame. Black Magic is well known to give the feeling that the ball sinks into the stringbed. Solinco Tour Bite or Signum Pro Tornado, however, are not known for great dwell time. However, the spin potential of Tour Bite is almost universally stated as being one of the greatest of all poly strings. So, if the amount of string bed contact is more or less the same across strings, let alone the same material, then no, dwell time does not increase spin potential.

I purposely didn't cherry pick. I included portions of the publication that showed where I was wrong. You say you can't increase the dwell time, but this publications stated they measured a dwell time increase of over 2x. Tell me again who's dense.

You obviously don't actually feel the ball on the strings. You feel the vibrations of the racket (racket/string system) which start as the ball contacts the strings and continues long after the ball has left the strings. A looser and/or more flexible string job will respond with lower frequency vibrations than a tighter stiffer string job. These vibrations will be correlated to the dwell time on the racket. Your brain can tell the differences between the vibrations, and then, through experience, will tell you that your are expericencing hitting the ball with a more flexible system (more rubber band-like) or a stiffer system (more iron-bar like).

I purposely didn't cherry pick. I included portions of the publication that showed where I was wrong. You say you can't increase the dwell time, but this publications stated they measured a dwell time increase of over 2x. Tell me again who's dense.

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Quote me where I said you cannot increase the contact time with strings. I not once said that, nor would I as it has nothing to do with the topic at hand. What I DID say was that simply increasing the contact time by a few ms does not increase the feeling of dwell time. Obviously if you string at 60lbs and then at 30lbs you will get a much different sensation. As is your MO, what that has to do with this discussion, I haven't the faintest idea.

You obviously don't actually feel the ball on the strings. You feel the vibrations of the racket (racket/string system) which start as the ball contacts the strings and continues long after the ball has left the strings. A looser and/or more flexible string job will respond with lower frequency vibrations than a tighter stiffer string job. These vibrations will be correlated to the dwell time on the racket. Your brain can tell the differences between the vibrations, and then, through experience, will tell you that your are expericencing hitting the ball with a more flexible system (more rubber band-like) or a stiffer system (more iron-bar like).

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Of course they will be correlated. Even that does not mean that the ball spent more time on the racquet, however. Since UCSF just posted a reference, I'll just refer to that whereby if you're rallying hard, you get the feeling of dwell time much more than on a drop shot volley even though the ball spends less time on the strings during the rally. The only point that I've been trying desperately to get across to the OP is that strings which exhibit the feeling of longer dwell time do not necessarily have greater spin potential. The reason is because actual contact times are so similar, and strings, racquets, swing speeds and tensions are all dissimilar among players, and yet the feeling of dwell time for certain strings is pretty much well accepted. In other words: the feeling of pocketing does not necessarily imply greater spin.

Thanks to all of you for helping me learn a lot. The biggest things I have learned are:

1. Never mention dwell time again.

2. Talk about ball pocketing instead. Objective laboratory ball pocketing, not subjective. Some of you seem to think ball pocketing increases spin potential. Maybe? It does for me because the "string/ball friction" is increased. I think of the strings wrapping around the ball like a v belt on a pulley. The greater the angle of wrap, the more "friction" is present.

3. A significant component of spin, particularly topspin as an example, is caused by the movement of the mains along the crosses during impact and their attendant spring back to their original position as the ball leaves the string bed. A minimal amount of "string/string" friction is best for this. More initial movement along the crosses is a good thing so long as the mains spring back to their original location.

4. The "string/string friction" example explains why my gut mains have so much less fraying with a smooth poly cross than with a gut cross.

5. We never got to the open versus closed stringbed, but I guess that can wait for another session. The open stringbeds would seem to have more ball pocketing for sure. Right?

Thanks again. Be sure and let me know if I have learned anything incorrect, as I am sure some of you will do.

I was watching the thread develop through out my work day, had no time to respond and was kinda waiting for the dust to settle anyways. Apologies for the long read. Hard to do a complex subject like this justice with a few sentences. Just three main topics for me here. 1 : Measuring Dwell and Deflection. 2. Dwell and Spin. 3. Dwell and Control.

Issue 1: Objectively Measuring Dwell Times & String Bed Deflection :

1a. One of the early statements in the thread that took the conversation into a very argumentative place was that dwell time could not be measured, is strictly a feeling, nothing more, therefore the term should be banished to the realm of the subjective, and dealt with entirely from that perspective alone. The data reveals ridiculously minor differences, but both Dwell time and string bed deflection are measurable. See screen grabs below. If you want to make a case that the differences are so minor that they are likely not perceivable to the player, or that dwell time isn't perceivable at all, then I just put $10.00 in to the basket on that sermon. If one's thesis is that dwell time has got very little to do with spin, amen to that my brother! But that's a whole 'nuther can of worms. Plenty of reasons to poo poo the concepts of pocketing and dwell time if one had the inclination, (many of which I agree with) but lack of objective measurements, isn't one of them. Not calling out PvAudio here, he's largely been the voice of reason and good information through out the whole thread, just pointing out this one dark corner of the TW University String Database that might have been overlooked.

1b. The dwell times read about 5-6 times longer than typical on court impacts of 4-6 ms. That's because the object striking the strings in the tests for stiffness, tension, deflection, etc. is a test hammer, not a ball. This is takes the ball out of the equation, and gets to the heart of what the string is doing. Balls lose pressure every second, change texture with repeated impacts etc... not good for getting clean data. One might choose to de - ligitimize the measured dwell times for this reason, but you'd have to throw out just about everything else we've measured too (stiffness, tension loss, deflection, energy return) in exactly the same way. Also worth a mention, notice the "actual pre - impact tension". This column demonstrates the tension after the string had a good number of whacks (I forget how many) with the test hammer, at levels simulating a 120 mph serve. Poly loses a bunch of tension in those pre-test whacks, while gut retains much more, yet still manages a deeper pocket and incrementally longer dwell times. Gut, thou art amazing.

1c. Pocketing and dwell times are often inversely related. You'd think that when the ball sinks very low into the strings, then it's going produce a longer dwell time. That's not always the case. QUOTE: "It's counter - intuitive but the harder you hit the ball, the shorter the dwell time. You somehow have a picture in your mind of a harder hit ball sinking deeper into the string bed, and therefore taking a longer time to come out. What actually happens is that the harder you hit the ball, the stiffer the strings get, as does the string plane. Even though the ball sinks in more, it also snaps back sooner due to the increase in string plane stiffness"-- Howard Brody, The Physics And Technology Of Tennis, Chapter 26.

[..]

Issue 2 : Dwell Time and Spin, IE.. "wrapping around the ball like a belt on a pulley"

2a. I follow your line of reasoning, and its a common thought process. You are thinking that deeper pocketing provides better grip on the ball, and better grip provides for more spin. It's a common conception but you have got some slightly faulty mental imagery. In the sport of table tennis, in which the ball does not squash, and the incidence angles are very steep, ball grip is a very big factor. In tennis however, not so much. Consider that the ball squashes flat like a bug on a windshield to roughly 1/2 its original size on impact. When you are able to see what actually happens with ultra high speed cameras, (See ITF Technical Video Provided) the tennis world becomes a strange and beautiful place indeed. The ball is a whole lot of shapes when it smashes into the racquet, but one shape it isn't, is round!. If the forces are great enough the ball can squash so firmly into the string bed that it's nearly flat, with the back of the ball bouncing off the front of the ball. The ball jiggles, the ball shakes and wobbles like a bowl of jello as it exits the string bed. Within this 4-6 ms time frame, all manner of strange things are occurring, and we... are utterly oblivious.

2b. We've learned within the last 5 years that spin enhancement is a product of 2 factors. ball-string friction (more is better), and string-string friction (less is better) Turns out, low inter string friction, is a much more important factor than ball "bite"

QUOTE 1: "Until recently, the prevailing theory regarding string stiffness and spin has been that the firmness and lateral rigidity of a stiffer string will create more ball-to-string friction due to more squashing and embedding, resulting in more spin. It is true that friction accounts for most of the spin produced by the stringbed, but it does not account for most of the difference in spin between stringbeds. Recent research suggests that lateral main string movement is the most important factor determining this difference." -- Crawford Lindsey, March 14, 2011

QUOTE 2 : "Recent experiments (Spin and Material, Spin and String Movement, Spin and String Pattern and String Snap-Back and Spin) have also demonstrated that sideways motion of the main strings during contact with the ball actually contributes to increasing spin. This sideways movement exerts a torque on the ball when it snaps back into position, thus causing topspin. Polyesters have been shown to add about 20% more spin than nylons. Polyesters can differ up to about 15% from each other in spin production while nylons might vary by 20% from each other. And the difference between the spiniest polyester and stickiest nylon is almost 50%. Virtually all this difference is attributable to the amount of torque supplied by the sideways movement and snap back of the main strings.The role of ball-string friction in this process is that it influences both the amount of lateral string movement and the torque the snap-back exerts on the ball (though the magnitude of its contribution is yet to be ascertained by experiment). It is here that ball-string friction contributes to the difference in spin performance between string models, but only if the strings move. Otherwise, ball-string friction produces about the same spin for every string. And whether the strings move or not depends on the static and sliding friction between strings. " -- Crawford Lindsey, August, 2011, Static Friction and Spin

QUOTE 3 : Summary Observations:
• All the polyesters had more spin than any of the nylons (a gut snuck in above some polys however).
• The average polyester spin compared to the average nylon is +20.2%.
• The difference in spin between the highest and lowest poly is +15.9%.
• The difference in spin between the highest and lowest nylon is +26.8%.
• The difference in spin between the highest string and the lowest string is +49.3%.-- Crawford Lindsey, String movement and Spin

2c. Getting the string to grip the ball is not a problem!. (See Video Below) The lab testing was performed by the International Tennis Federation. I've seen many slow motion impact vids. This one is the most dramatic. The others show the ball smashing to about to about 1/2 original size.

3A. Some players opine that longer dwell times increase control. Not only is there no experimental evidence for this, it runs counter to the age old truism accepted by both academics and players ... "string tight for control, loose for power".

Excellent post, ChicagoJack. I think, however, the problem was simply a matter of wording. When people talk about dwell time and pocketing, they're almost always talking about the feeling that the ball is sinking into the stringbed. The only point I was trying to make is that the difference in stringbed contact time between strings is absolutely minimal. When you search around for dwell time, you get results with people saying strings have great dwell time or pocketing. That's a feeling, and as shown in your measured results, the difference between strings is only on the order of milliseconds, so there is no way you're feeling an appreciable increase in stringbed contact. That's where the thread got off on the wrong track, I never said that the time that the ball spends on the stringbed isn't measureable. If it wasn't, then there would be no way that I would know just how short of a time it's there

PVAudio - Yeah cool man, totally understand BTW agreed with most of all your comments within. It's really hard to talk about this stuff in a productive way when the same terms mean so many different things to different people.

Yes, I am an admitted data nerd. Nothing soothes my soul more than looking at nicely organized columns of digits, and attempting to understand the secrets held therein. On the other hand, I am a tennis player too. I get it. I feel what I feel. One of my frames is strung with Dunlop Black Widow 18 at 54lbs. When I'm returning a big server who can dish out lots of pace and rpms, it just seems like the ball stays in the stringbed forever, first sliding, then unwinding whilst I undo all the spin of the incoming ball, and attempt to reverse it with my own top spin and send it back. I can certainly understand why peeps search for a way to describe this sensation which seems to last forever and settle on dwell time.

What is actually happening is most of the impact sensation you feel (especially when you contact outside the sweet spot, and especially near the tip) is the residual frame vibration that occurs well after the ball exits the string bed. I could explain more about that, but that last post wore me out. Another day perhaps.

Agreeing on the definition of terms is essential to a rational discussion.
If you don't, you're arguing at cross purposes.
I think that's what happened here.
Tennis is not a science, no matter how much some of us wish it were.

ChicagoJack, that is a very interesting video clip! It certainly looks more extreme than my mental picture of a typical shot and would change how I visualize ball-string interaction, except that I wonder how fast the ball was traveling and how the racket was anchored. Also, isn't that a pressureless Tretorn Micro-X ball which may not react like a normal ball?
Most slow-mo clips of pros hitting do not appear to show so much ball deformation, but they are also not so detailed.

Rough poly is exploiting the ball-string friction parameter. The higher this is, the greater the spin potential. The lower the string-string friction, the greater the spin potential. Interestingly, we have two counter examples to look at then using the same set of data. A stiffer string, according to TWU data, is more likely to be a better spin string. Thereby poly will provide more spin potential than synthetic gut or multifilaments. However, a moreelastic string will also provide more spin potential. These two concepts are not the same. To make it more clear, let me define the two. Stiffness is the ability for a material to not deform or to resist deformation when under stress. Elasticity is the ability for the material to return to its original state after being deformed by stress. So, we're at an impasse: we want a string which does not deform under stress, but one which when it does deform, it returns to its original shape. This is why polyester is so popular for spin. It is very stiff, but yet it has a surprising amount of elasticity.

Once that elasticity is gone from usage, then the string's performance is lessened. If you have a rough string which can hold onto the ball while the string is deforming, you can return more energy to it. BUT! If the sliding friction is too high, or the friction trumps the string's elasticity, then it doesn't matter as much. That's why while natural gut is overall the best for spin next to poly, it still suffers from high string-string friction. Therefore, you want something with elasticity in the mains that bites onto the ball and something smooth in the crosses so that the mains can move more freely. This is the reasoning behind the gut/poly hybrid. If you put a rough poly main with a smooth poly cross, you can theoretically get similar results: you get great stiffness from the mains, and good ball-string friction, and low sliding friction just like with gut/poly.

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If a more elastic string that slides more is better for spin then why does kevlar which is very stiff and non elastic put so much spin on the ball? When I go from kevlar to a all poly set up it seem like I get just as much spin if not more from the kevlar, but more power from the poly.

If a more elastic string that slides more is better for spin then why does kevlar which is very stiff and non elastic put so much spin on the ball?

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That was exactly my point, it's a conundrum. Greater stiffness yields higher spin potential, but greater elasticity also yields higher spin potential. My theory, which is my reasoning alone, is that gut yields good spin because it is so elastic that it's able to overcome a lot of the string-string friction. Kevlar, which has extraordinary ball-string friction will also yield good spin potential. Whether this is true or not, I have no idea, but I DO know that it's because poly can combine the best attributes of both of these string types and meet in the middle that it's far superior than either with regards to spin potential.

That was exactly my point, it's a conundrum. Greater stiffness yields higher spin potential, but greater elasticity also yields higher spin potential. My theory, which is my reasoning alone, is that gut yields good spin because it is so elastic that it's able to overcome a lot of the string-string friction. Kevlar, which has extraordinary ball-string friction will also yield good spin potential. Whether this is true or not, I have no idea, but I DO know that it's because poly can combine the best attributes of both of these string types and meet in the middle that it's far superior than either with regards to spin potential.

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That makes some sense, but I am not so sure that poly can really exceed kevlar in spin potential let alone be far superior. I feel that because poly puts more power on the ball that many players will see a better hop off the court because of the polys power not spin, so then many would think they are getting more spin but actually it is more power.

If we are talking about just spin I think that kevlar actually produces more spin than poly.

Actually, thinking about it more, I would bet Kevlar works because it is highly resilient. I know, more boring terms, but resilience is the ability for something absorb energy when it is deformed elastically. It is the ratio of yield strength squared to young's modulus. Not going to get into that, BUT, the yield strengh of Kevlar is extremely high, and if it's a squared term, that could negate the high Young's modulus if it's a lower order. This is pure speculation on my part.